(OPRAH.com) -- A client I'll call Sharon knew that something was missing in her marriage. She and Robert used to be passionate about each other, she said, but after 12 years and two children, she felt removed. Robert never asked her about work or what she was worried about or felt like doing. She was no longer attracted to him, and they rarely spent time alone together.

If friends confide more to each other than to their spouses, they are having an emotional affair, expert says.

Instead, she threw her energy into raising the children and her job as a paralegal. Life had become bland.

Then there was Todd. He'd been at the law firm longer than Sharon and showed her the ropes. They would discuss complicated cases, and Sharon found his enthusiasm engaging. They'd grab coffee together, and soon coffee became lunch, and lunch led to phone calls and e-mails as their conversations went from professional to deeply personal.

Sharon thought about Todd all the time, and told me she hadn't felt this alive since she and Robert had started dating. While she recognized a crush her excitement about seeing him, her pleasure in his jokes, her relief in confiding in someone who got her -- she told herself there was nothing wrong with what she was doing because they weren't having sex. Oprah.com: The new face of infidelity

Robert, however, started to notice his wife's coming home later. She was on her cell phone a lot on the weekends, and when he asked who she was talking to, she became evasive. At one point, he complained that they never had sex anymore, that he felt lonely in the marriage, and that he wondered if there was someone else.

Sharon assured Robert -- and herself -- that she wasn't having an affair. While she felt a little guilty, the thought of giving up Todd, the way he made her feel beautiful and funny and fantastic, was unbearable.

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Emotional cheating (with an "office husband," a chat room lover, or a newly appealing ex) steers clear of physical intimacy, but it does involve secrecy, deception, and therefore betrayal.

People enmeshed in nonsexual affairs preserve their "deniability," convincing themselves they don't have to change anything.

That's where they're wrong. If you think about it, it's the breach of trust, more than the sex, that's the most painful aspect of an affair and, I can tell you from my work as a psychiatrist, the most difficult to recover from. Oprah.com: How to affair-proof your marriage

Few people go looking for an extramarital entanglement. But like Sharon, they might hit a patch where their relationship isn't fun anymore, and they feel isolated and frustrated. Rather than making a collaborative effort with their partner -- and perhaps a couples therapist -- to improve it, women in particular often accept that "this is just the way the marriage is."

So while they aren't consciously in the market, they are ripe for an affair of the heart: hungry for attention, craving excitement, and eager for someone to fill the emptiness they feel inside.

Sharon came to depend on Todd for emotional highs. The flirting, the accolades, the sympathetic ear all made her feel special. She escaped into this new involvement in a scenario that's increasingly common.

Though emotional affairs have always been around, I'm seeing more of them among my clients than ever before. We've all grown so used to watching, reading, and hearing sexually suggestive material that there's no longer an obvious verbal or physical line we think we're crossing.

And the exponential growth of e-mail, instant messaging, and cell phones gives us a wealth of private ways to connect. It's a snap to Google an old flame: What would have been idle fantasy a decade ago can, with the click of a mouse, grow into emotional (or sexual) infidelity.

We all know men and women who really are "just friends," and there's usually some romantic frisson, even if neither party admits it. But a healthy male-female friendship isn't clandestine. Oprah.com: Can men and women be just friends?

Once a man and woman avoid telling their partners how much time they're spending on the friendship, make sure they look great anytime they're going to be together, or confide more in each other, including marital dissatisfactions, than in their spouses, they're involved in an emotional affair.

Often I'm told of a friendship that hasn't gone that far...yet. But if the possibilities are tempting, I believe that's the moment to look more closely at the marriage. What is each spouse missing that he or she needs?

My prescription is for them to ask directly and answer frankly, because from everything I've seen, when a couple can't express their feelings, concerns, and dreams, they're both at risk for betrayal. I frequently talk to couples in this vulnerable state, not only about how to reclaim closeness but also how to protect their relationship from third parties. Even when a marriage can't be salvaged, I'd rather see it end amicably before either person starts up with someone new.

Three habits strike me as playing with fire: (1) flirting with others, which can become too intoxicating to give up, (2) "innocently" spending time alone with old lovers, and (3) hanging out with emotional cheaters who make what they're doing seem like no big deal.

Increasingly, I find people are already enmeshed in an affair of the heart by the time they contact me, and they are terribly torn. They have a very hurt spouse but can't bear to lose their "friend." Marital implosion is close at hand.

My approach seems like tough love, but I'm convinced it saves a lot of grief. The first and most important task, from which all the other things these clients must do will follow, is to take responsibility for the affair -- same as if they'd had a sexual liaison. Denying it or blaming their partner's inattentiveness prevents the couple from re-engaging.

The only cases where it might not be best to fess up are the rare ones where the partner has no suspicions: Revealing hidden feelings just to absolve guilt is not a great idea.

Second, the affair must end. Yes, it hurts. And no, it's not possible to disengage partway and still be pals. Things get trickier if the infidelity began in the workplace, but all future interaction must be purely professional and kept to an absolute minimum.

Third, I try to help clients unearth the reasons they got overinvolved. Was their marriage failing? Did they need to build their self-esteem? Were they repeating the pattern of a parent who cheated? To prevent an encore, they must be brutally honest with themselves.

Finally, they have to build back the trust, which is the biggest obstacle to saving the marriage. I'm constantly telling people that it requires a lot of time, openness, and accountability (for example, being clear about whereabouts and coming home right after work).

What I find to be remarkably consistent is that most people don't appreciate the relationship they do have until they're about to lose it. This is what happened with Sharon. When Robert found her e-mails to Todd ("I miss you so much...I can't wait to see you," along with complaints about her home life), he was shattered and wanted a divorce.

As soon as Sharon realized her husband might leave her, Todd didn't seem quite as thrilling. But saying goodbye to him, which she ultimately decided to do, was wrenching, and Robert isn't sure whether he can forgive her. The three of us are still working on understanding why the affair happened and whether they can agree to rebuild their relationship.

It's much more difficult to make your way back from a betrayal of intimate feelings than to try to refresh a marriage that may have become flat and distant.

When you ignore anxiety-inducing thoughts like "I feel stuck -- I wish I could run off and have fun or I feel old and dumpy -- if only someone would make me feel young and sexy again," you cannot examine or deal with them in a productive manner.

Instead, you unwittingly act them out, with potentially devastating results. Any good relationship takes an investment of time, effort, and emotional energy. What few people want to accept is that we can all become Sharon and Robert, and that marriage, while potentially tremendously gratifying, is always a work in progress. Oprah.com: How to save your relationship